1. Field of the Invention
The present invention relates generally to a chassis dynamometer for performing a bench test of performance of an automotive vehicle. More specifically, the invention relates to a control system for a chassis dynamometer which is particularly applicable for a road test simulating bench test for a four wheel drive type automotive vehicle.
2. Description of the Background Art
Japanese Patent First (Unexamined) Publication (Tokkai) Showa 63-55433 discloses a chassis dynamometer for a four wheel drive type automotive vehicle. The disclosed chassis dynamometer employs rollers for four respective vehicular wheels, a power absorber device and a mechanical inertia device. Clutches are provided for connecting left and right rollers for synchronizing two front rollers and two rear rollers respectively by engagement of clutches. Namely, the chassis dynamometer disclosed in the above-identified publication is operable in two distinct modes. When the clutches are disconnected, the left and right wheels operates independently of each other for independent operation of the four respective rollers. When the clutches are engaged, synchronous operation between respective left and right rollers is achieved. In such case, front and rear pairs of rollers are operative independently of each other. In the disclosed system, distribution of the driving torque for respective rollers is controlled as a function of acceleration of the overall unit of the chassis dynamometer. In derivation of a torque different between front and rear rollers, specific inertia, i.e. mechanical inertia, of front and rear wheels is not taken into consideration.
A similar type of chassis dynamometer has been proposed in Japanese Patent First (Unexamined) Publication (Tokkai) shows 61-734 and Japanese Patent First (Unexamined) Publication (Tokkai) Heisei 2-46891. In the latter two publications, a component of mechanical inertia is not taken into account. Since a vehicle is always subject to mechanical inertia, failure to monitor mechanical inertia may cause test accuracy to be degraded. In other words, the systems set forth above cannot precisely simulate a road test because distribution of driving torque to respective rollers may be differentiated from actual road test data due to lack of the mechanical inertia factor.
On the other hand, in order to simulate behavior of the four wheel vehicle, it becomes necessary to simulate load distribution between front and rear axles. That is, during actual driving of the vehicle, the vehicular attitude can be changed by shifting of the center of gravity affected by inertia moment. Typical attitude change are known as winding up or squatting and nose diving, which are caused by axial shifting of the center of gravity. Conventionally, such vehicular attitude changes have not been possible to simulate. The aforementioned Japanese Patent First Publication Showa 63-55433 provides a certain gain in simulating vehicular pitching motion by providing the capability of operating the front rollers and rear rollers independently of each other. However, even by utilizing such a chassis dynamometer, it has not yet been possible to successfully simulate nose diving caused by an inertial moment of a vehicular body.
On the other hand, in modern automotive technologies, it has been becoming important to simulate vehicular body attitude change for testing performance of an attitude control system to be installed in the vehicle. For instance, capability of simulating nose diving will permit testing and evaluation of performance of the anti-skid brake control systems. In the current technology, nose dives may be simulated by providing a load distribution control system for the vehicle or otherwise by utilizing special arrangements of a chassis dynamometer which is specifically designed for simulating nose dives.
There are two types of four wheel drive power train arrangements to be employed in the vehicle. One of those is a full-time four wheel drive power train layout, in which driving torque generated by an automotive engine is always distributed to all four wheels. The other is a part-time four wheel drive power train layout, in which the power train normally operates as a two wheel drive power train, and switches to four wheel drive under predetermined conditions, such as excessive wheel slippage of the primary drive wheels. In case of the part-time four wheel power train layout, since the vehicle is normally driven by a two wheel drive power train layout, simulation is substantially the same as that for a two wheel drive vehicle. Also, even when the part-time four wheel power train is switched into four wheel mode due to excessive wheel slippage at the primary driving wheels, since the wheel slippage may easily be caused even in the four wheel drive mode power train layout both on the primary and auxiliary driving wheels, the simulation will not be significantly different from conventional two wheel drive vehicles. However, on the other hand, in the modern full-time four wheel power train layout, distribution of driving torque is variable depending upon vehicular driving conditions. Typically, torque distribution is adjusted in proportion to acceleration and deceleration. When bench testing is to be performed on a chassis dynamometer for such a vehicle having a variable torque split full-time four wheel drive power train layout, for simulating straight acceleration and deceleration on a smooth road, wheel speeds at front and rear wheels will become different. At the same time, the rotation speed of the roller as an imaginary road surface is required to be equal for all rollers. Particularly for performing a 10 mode test or an LA-4 mode test for testing fuel consumption and exhaust gas composition, uniformity of roller speed becomes essential for providing satisfactory testing accuracy.
Namely, in case of a four wheel drive vehicle having a passive differential mechanism, such as a center differential gear unit, wheel speed at the front and rear wheels should be different because ground speed at all wheels are equal to each other. Naturally, increasing of the wheel speed difference between the front and rear wheels may increase internal loss of driving torque in the center differential gear unit and may influence exhaust gas composition and fuel consumption. On a chassis dynamometer, there also exists wheel slippage characteristics similar to those occurring on an actual road surface. Therefore, it is considered that, by adjusting the peripheral speed, that is, the rotational speed of the outer surfaces of the rollers to be consistent with each other, torque distribution similar to that on an actual road can be simulated.
In an actual road test, overall driving torque at four wheels can be expressed by the following equation: EQU F=A+Bv.sup.2 +Mg.times.(dv/dt)+Mgsin .theta. (1)
wherein
F: vehicular driving force; in case of four wheel drive vehicle, total driving force of driving forces at respective of four wheels; PA1 A: rolling resistance of the wheel; PA1 B: coefficient of air resistance; PA1 v: vehicular speed (m/sec.) PA1 M: vehicular inertia weight (kg) PA1 g: gravitational acceleration; and PA1 .theta.: inclination angle of the road surface in the longitudinal direction. PA1 at least one roller rotatably coupled with a vehicular wheel, said roller to be driven by driving torque transmitted from said vehicular wheel; PA1 at least one dynamometer coupled with the roller to be driven by driving torque transmitted through the roller; PA1 first monitoring means for monitoring preselected control parameters for providing first chassis dynamometer control data; PA1 second monitoring means for monitoring rotary components in a system associated with the dynamometer including the dynamometer per se, for providing second chassis dynamometer control data; PA1 control signal generator means for receiving the first and second chassis dynamometer control parameters for deriving a dynamometer control signal for generating a control signal to said dynamometer providing a rolling resistance to said vehicular wheel at said roller simulating a predetermined vehicular driving condition. PA1 at least first and second rollers rotatably coupled with first and second vehicular wheels oriented at axially different position on a vehicular body, said rollers being driven by driving torque transmitted from said vehicular wheels; PA1 at least first and second dynamometers respectively coupled with the first and second rollers to be driven by driving torque transmitted through an associated one of said first and second rollers; PA1 first monitoring means for monitoring preselected control parameters associated with the first roller, for providing first chassis dynamometer control data; PA1 second monitoring means for monitoring preselected control parameters associated with the second roller, for providing second chassis dynamometer control data; PA1 third monitoring means for monitoring rotary components in a system associated with the first dynamometer including the first dynamometer per se, for providing third chassis dynamometer control data; PA1 fourth monitoring means for monitoring inertial force of rotary components in a system associated with the second dynamometer including the second dynamometer per se, for providing fourth chassis dynamometer control data; PA1 control signal generator means for receiving the first and third chassis dynamometer control data for deriving a first dynamometer control signal for generating a control signal to said first dynamometer providing a rolling resistance to said vehicular wheels of said first roller simulating predetermined vehicular driving condition and for receiving the second and fourth chassis dynamometer control data for deriving a second dynamometer control signal for generating a control signal to said second dynamometer providing a rolling resistance to said vehicular wheels at said second roller simulating predetermined vehicular driving condition. PA1 a first roller rotatably coupled with the primary driving wheel to be driven by driving torque transmitted therefrom; PA1 a second roller rotatably coupled with the auxiliary driving wheel to be driven by driving torque transmitted therefrom; PA1 at least first and second dynamometers respectively coupled with the first and second rollers to be driven by driving torque transmitted through an associated one of said first and second rollers; PA1 first monitoring means for monitoring preselected control parameters associated with the first roller, for providing first chassis dynamometer control data; PA1 second monitoring means for monitoring preselected control parameters associated with the second roller, for providing second chassis dynamometer control data; PA1 third monitoring means for monitoring inertial force of rotary components in a system associated with the first dynamometer, including the first dynamometer per se, for providing third chassis dynamometer control data; PA1 fourth monitoring means for monitoring inertial force of rotary components in a system associated with the second dynamometer including the second dynamometer per se, for providing fourth chassis dynamometer control data; PA1 control signal generator means for receiving the first and third chassis dynamometer control data for deriving a first dynamometer control signal for generating a signal to said first dynamometer providing rolling resistance to said vehicular wheel associated with said first roller simulating predetermined vehicular driving condition and for receiving the second and fourth chassis dynamometer control data for deriving a second dynamometer control signal for generating a signal to said second dynamometer providing rolling resistance to said vehicular wheel associated with said second roller simulating a predetermined vehicular driving condition.
Normally, if the testing is performed simulating a flat road, the element (mgsin .theta.) can be neglected. The element (A) and element (Bv.sup.2) are absorbed by the dynamometer or by a power absorbing device. On the other hand, the element (mg(dv/dt)) is absorbed by a mechanical inertia control device, such as a flywheel or electrical inertia control means as disclosed in the above-identified publications. Especially, as illustrated in the aforementioned publication, electrical inertia control means is frequently employed. This is because the mechanical inertia of the roller and power absorbing device becomes approximately double that of a two wheel drive vehicle. For instance, in case of a chassis dynamometer having rollers of 1591 mm in diameter, the mechanical inertia of the roller and a power absorbing device will be in a range of 400 kg to 500 kg in case of a two wheel drive vehicle and in a range of 800 kg to 1000 kg in the case of a four wheel drive vehicle. Since the overall weight of a general small size vehicle is in a range of 800 kg to 1300 kg, it is almost equal to the mechanical inertia of the mechanical inertia absorbing device. Since the mechanical inertia in the electrical inertia absorbing means has much smaller mechanical inertia, the electric inertia absorbing means are advantageously employed.
On the other hand, concerning a composite ratio of traveling resistance, the elements (A) and (Bv.sup.2) which are called as constant speed traveling resistance will not exceed 500N at vehicle speeds lower than or equal to 80 km/h. On the other hand, the traveling resistance of the element (Mg(dv/dt) at accelerating state in a magnitude of 0.1 g and at 1000 kg of the overall vehicular weight, becomes approximately 980N and therefore greater than that of the constant speed traveling resistance.
Accordingly, in such testing including testing for acceleration and deceleration, the technologies disclosed in the aforementioned publications are applicable only for a 50:50 torque split ratio. For this reason, the speed difference control disclosed in the aforementioned Japanese Patent First Publication Showa 63-55433, becomes substantially low in response for the vehicle having torque split ratio far different from even distribution (50:50).